1. Field of the Invention
The present invention relates to an alkyl acrylate copolymer. More particularly, it relates to a copolymer comprising a main component of an alkyl acrylate and a polyfunctional monomer component having conjugated double bond and non-conjugated double bond and optionally a comonomer component or a copolymer obtained by graft-copolymerizing monomers on the copolymer.
2. Description of the Prior Arts
As well-known, the resins obtained by graft-copolymerizing styrene, methyl methacrylate or acrylonitrile on a polybutadiene rubber (hereinafter referring to as ABS resin) are copolymers having excellent impact strength and fabricability . However, ABS resins are disadvantageously deteriorated by ultraviolet rays because of double bonds of the butadiene component.
The resins obtained by graft-copolymerizing styrene, methyl methacrylate or acrylonitrile on a crosslinked polyacrylate elastomer (hereinafter referring to as AAS resin) have been proposed as the resin having improved weathering durability without deteriorating excellent impact strength of ABS resins. The AAS resins have the improved weathering durability however, they have not satisfactory impact strength and fabricability.
The rigid thermoplastic resins such as vinyl chloride resins, chlorinated vinyl chloride resins, methacrylate resins, styrene-acrylonitrile copolymers, .alpha.-methylstyrene-styreneacrylonitrile copolymer and polycarbonates are brittle by impact whereby ABS resin or AAS resin has been blended to the rigid thermoplastic resin. However, when ABS resin is blended, the weathering durability is remarkably inferior because of the double bonds of the butadiene component which are deteriorated by ultraviolet rays. Accordingly, the compositions are not suitable for using outdoor for a long time. On the other hand, when AAS resin is blended, the impact strength and fabricability are not satisfactory.
The inventors have considered that either or both of the crosslinkage of the elastomer or the graft-copolymerization is not suitable to cause the disadvantage in the case of AAS resins, and have proposed the graft copolymers produced by using the elastomer trunk polymer produced by adding a small amount of a conjugated diolefin to an alkyl acrylate and a crosslinking agent (U.S. Pat. No. 3,959,408).
The graft copolymer imparts satisfactory impact strength and fabricability and also improved weathering durability in comparison with that of the composition blending ABS resin even though a small amount of the conjugated diolefin is added. However, the weathering durability is sometimes slightly inferior to that of the composition blending AAS resin. The inventors have further studied to improve it.